1. Field of the Invention
The present invention relates generally to the remote application of therapeutic radiated energy. In particular, the present invention provides a method for applying High Intensity Focused Ultrasound to reduce internal bleeding.
The use of ultrasound for imaging and diagnosis of disease is well known in the medical field. Ultrasound imaging generally relies on differences in the reflection of high frequency acoustic waves by organ, and soft tissues. Ultrasound waves, when applied at power levels required for imaging, have been found to be free from the deleterious side effects associated with many other forms of radiated energy, such as X-rays, microwaves, and other electromagnetic fields. Hence, ultrasound imaging systems have a distinct safety advantage over other known imaging modalities.
Generally, imaging ultrasound waves are radiated from a transducer which also senses the reflections. Imaging ultrasound transducers often make use of multiple radiating and/or receiving radiating surfaces. For example, modern ultrasound probes often use precise timing control over a series of active surface regions, referred to as a phased array, to control the radiation direction and to sense the source of reflections. Ultrasound imaging systems having multiple transducer surface regions have found particular use in Doppler measurements of internal blood flows. Ultrasound Doppler imaging systems make use of multiple ultrasound pulses to non-invasively monitor internal movements. Doppler imaging typically relies on the frequency shift of acoustic reflections from moving matter, and also on the change in position of discrete masses between pulses. Doppler colorflow imaging indicates relative speeds of motion by assigning a range of false colors for the measured speeds. Ultrasound Doppler systems may scan a single sector of tissue, or may scan in multiple orientations to provide three-dimensional imaging. Array transducers facilitate Doppler imaging by providing electronic scanning through control of the phase of excitation provided to the discrete regions of the array.
Although ultrasound imaging is noted for its safety, ultrasound energy applied at higher power densities can have significant physiological effects on tissues. These physiological effects may result from either thermal or mechanical effects of ultrasound energy. Thermal effects of ultrasound include localized heating, hyperthermia, and ablation of tissue (with relatively low energy levels), and even rapid high temperature searing. Mechanical effects include breaking-up of solid objects, liquefaction of tissues, and cavitation.
These effects of high power ultrasound can occur adjacent the ultrasound radiating surface, or they may be produced at a distance from the radiating surface by focusing of the ultrasonic waves at a target region within the tissue. For example, lithotriptors use a large external radiating surface to focus short bursts of ultrasound energy as shock waves inside a patient body, thereby mechanically fragmenting kidney stones. Clearly, the ultrasound energy must be focused on a target region which is very small relative to the transmitting surface to avoid affecting the intermediate tissue.
The use of High Intensity Focused Ultrasound (herein referred to as "HIFU") has previously been proposed as a therapy for a number of diseases which manifest themselves in a localized or "focal" manner. Focal diseases for which HIFU has been suggested include, for example, neoplastic and other diseases of or in the brain, breast, liver, and prostate. Although surgical procedures have been developed for these diseases, HIFU therapy potentially offers a non-invasive or minimally invasive alternative, thereby inflicting much less trauma on the patient, and promoting faster healing. For example, HIFU therapy is now available as a treatment for Benign Prostatic Hyperplasia, allowing the remote ablation of hyperplastic tissue without physical penetration of the urethra and prostate, thus reducing the risk of infection.
Parent U.S. application Ser. No. 08/446,503, entitled "Multifaceted Ultrasound Transducer Probe System And Methods For Its Use", filed May 22, 1995, the full disclosure of which is herein incorporated by reference, describes an exemplary HIFU system and method for the treatment of BPH and other focal diseases. This exemplary HIFU system includes a probe housing containing a multifaceted therapeutic transducer member and a servo system for aiming the transducer member within the probe. The transducer member has a plurality of radiating surfaces having different focal lengths and different radial orientations. Power is transmitted to alternative radiating surfaces to select a target depth. Additionally, an independent inner region of each radiating surface allows further variation in the target depth by manipulating the inner region's power supply phase relative to the surrounding outer region, the inner and outer regions acting as a simple phased array. An imaging transducer is also carried on the transducer member, allowing a single servo system to select the focal depth, aim the therapeutic surface, and scan the imaging transducer.
Although the above described HIFU system and probe have proven highly effective as a tool for applying HIFU therapy to focal diseases, the HIFU methods and systems proposed to date suffer from certain limitations. Specifically, HIFU treatments have generally relied only on the thermal and mechanical effects of ultrasound energy on fixed tissues and structures. The potential application of therapeutic ultrasound energy on body fluids, particularly for the coagulation of blood to control internal bleeding, has not previously been explored.
One of the most common causes of the death of trauma victims, both military and civilian, is internal bleeding. Broadscale internal bleeding is difficult to detect, has few well-recognizable symptoms, and can lead to death within a time ranging between minutes and several days. Blunt trauma often leads to hemoperitoneum from a rupture of the blood supply system of the abdominal organs and tissues, thus causing leakage of blood into the abdominal cavity and surrounding tissues. The organs most commonly injured include the liver, spleen, and kidneys. The survival rates from trauma victims with hemoperitoneum has been found to increase dramatically when proper care is provided soon after the injury.
The survival rate of trauma victims who survive long enough to receive state-of-the-art medical care at a major medical facility is relatively good. Once at such a facility, intra-abdominal fluid is often detected using Diagnostic Peritoneal Lavage (DPL). DPL is an invasive procedure having a complication rate of as high as 5%, typically from bowel or bladder perforation. Although ultrasound Doppler imaging offers a non-invasive diagnostic alternative, invasive therapies are generally required after diagnosis to control any significant internal bleeding.
Unfortunately, facilities capable of invasive surgical procedures, including DPL and abdominal surgery, are often a considerable distance from the injury site, requiring considerable transportation time. Additional time after arrival at a surgical facility is required for preparation of the patient, staff, and medical equipment for surgery. Meanwhile, the internal bleeding continues, as well as the associated risk to the trauma victim.
For these reasons, it would be desirable to provide methods and system for identifying, targeting, and controlling of internal bleeding, preferably without the damage to surrounding or intervening tissue associated with surgical intervention. Preferably, such methods would provide hemostasis sufficient for the transport of patients to a critical care facility, where more conventional surgical and diagnostic techniques are available. Ideally, these methods and systems for production of coagulation would be suitable for emergency rooms, local clinics, and even paramedics in the field. It would be best if such methods and systems could make use of the advances in imaging and therapeutic ultrasound technologies which have previously been applied to focal diseases.
2. Description of the Background Art
U.S. Pat. No. 5,322,055 describes an ultrasonic clamp which coagulates tissues within a scissor-like jaw as it cuts. U.S. Pat. No. 5,013,312 describes an ultrasonic scalpel having an integral bipolar electrode to coagulate as it cuts.
U.S. Pat. No. 5,207,672 describes the use of laser energy to cause coagulative necrosis of compressed prostatic tissue. U.S. Pat. No. 5,269,778 describes the use of a variable pulse width laser to penetrate tissue and effect deep coagulation.
U.S. Pat. No. 5,052,395 describes an ultrasonic pulse Doppler cardiac monitor which measures blood velocity. U.S. Pat. No. 5,152,294 describes a three-dimensional ultrasonic scanner. U.S. Pat. No. 5,186,175 describes a two-dimensional ultrasonic diagnostic array. U.S. Pat. Nos. 5,379,642, 5,255,682, 4,945,915, 4,155,260, and 5,050,588 are generally relevant.
C. Delon-Martin et al., Venous Thrombosis Generation by Means High-Intensity Focused Ultrasound, Ultrasound in Medicine and Biology, 21:113 (1995) describes a HIFU for sclerotherapy of superficial varicose veins. Vein walls were specifically targeted for thermal ultrasonic therapy, leading to temporary vein occlusion.
V. Zurinski et al., Real-Time Sonography with the Linear Array Scanner Multison 400, Electromedica 46, No. 4 (1978); R. D. Selbie et al., The Aberdeen Phased Array: A Real-Time Ultrasonic Scanner with Dynamic Focus, Medical and Biological Engineering and Computing, 18:335 (May 1980); O. T. von Ramm et al., Thaumascan: Design Considerations and Performance Characteristics, Ultrasound in Medicine, 1:373 (October 1974); D. Latham King, Real-Time Cross-Sectional Ultrasonic Imaging of the Heart Using a Linear Array Multi-Element Transducer, The Journal of Clinical Ultrasound, 1:196 (1973) are also generally relevant.